This invention relates to an eccentric orbiting reducer where the speed reduction is achieved by eccentrically revolving the pinions.
In general, the eccentric orbiting reducer has been used in various applications, especially as a reducer for robotics, because it is compact and yet provides a high reduction ratio.
However, the eccentric orbiting reducer 11 available on the market has a shortcoming in that its rigidity in the rotational direction, which is an important property of a reducer for robotics, is low because the radial distance L between the crankshaft 12 and the center axis Z of the reducer 11 is relatively short as shown in FIG. 3.
One possible idea for solving such a problem would be to use larger diameter gears for both the external gear 14 fixed on the crankshaft 12 and a drive gear 15 that meshes with the external gear 14 in order to increase the above-mentioned radial distance L as shown in FIG. 4, thus improving the rigidity of the reducer 11 in the rotational direction.
However, such a reducer 11 with a large diameter external gear 14 and drive gear 15 has problems such that it has a large inertia moment because of large gears, so that it tends to generate substantial vibration during acceleration and deceleration and it also requires a larger servomotor to drive the drive gear 15. Moreover, since the external gears 14 and the drive gear 15 are large, it can create interference with the external gear 14 in the circumferential direction and noise due to a high circumferential speed.
The present invention intends to provide an eccentric orbiting type speed reducer that produces little vibration and noise, while it is capable of easily improving its circumferential rigidity although it is compact and economical and is also capable of having its drive gear concentric with the center axis of the reducer while increasing the radial distance L.
An eccentric orbiting type speed reducer, constructed as a preferred embodiment of the present invention, comprises: a cylindrical member having internal gear teeth on its inner circumference; pinions having external gear teeth that mesh with the internal gear teeth each having a number of teeth slightly less than the internal gear teeth; a carrier having pillars that penetrate through the pinions in an axial direction; multiple crankshafts that are arranged equiangularly in a circumferential direction, are rotatably supported by the carrier at both axial ends, penetrate through the pinions in the middle, and cause the pinions to eccentrically revolve when they rotate; external gears each fixed on one end of a respective one of the crankshafts; a drive gear located in a position surrounded by the external gears; and multiple idler gears, each of which is rotatably supported by the carrier to be located between a respective one of the external gears and the drive gears to mesh with those gears, wherein the rotation of the drive gear is transmitted through the idler gears and the external gears to the crankshafts to cause the pinions to revolve eccentrically as well as to reduce the eccentric rotation of the pinions by means of the external and internal gear teeth, so that the cylindrical member or the carrier can rotate at a slow speed.
By having idler gears that mesh with the external gears fixed to the crankshafts and the drive gear between them, the reduction of the diameters of the external gears and the drive gear can be easily achieved. As a consequence, the inertia moment of the drive gear as well as vibration during acceleration and deceleration become smaller, hence reducing the size of the servomotor as well. The reduction of the diameters of the external gear and the drive gear also reduces the circumferential speed of the external gears and the drive gear, which in turn reduces noise to improve the working environment. Having idler gears increases the distance between the crankshaft and the reducer center axis of the reducer in the radial direction, which contributes to an easy improvement of the rigidity of the speed reducer in the circumferential direction.
In order to rotate the pinion smoothly, it is necessary to have the rotating phases of the three crankshafts match completely, but the above-mentioned requirements can be satisfied as long as the assembly condition described in claim 2 is satisfied.
The present disclosure relates to the subject matter contained in Japanese patent application No. Hei. 2000-29478 (filed on Feb. 7, 2000), which is expressly incorporated herein by reference in its entirety.